1. Field of the Invention
The present invention relates to various sensors (MEMS sensors) manufactured by an MEMS (Micro Electro Mechanical Systems) technique.
2. Description of Related Art
An MEMS sensor, having been recently loaded on a portable telephone or the like, is watched with interest. For example, a silicon microphone (an Si microphone) is a typical MEMS sensor.
The silicon microphone includes a silicon substrate. A through-hole passing through the silicon substrate in the thickness direction is formed in the central portion of the silicon substrate. A diaphragm made of polysilicon is provided on the silicon substrate to be opposed to the through-hole. The diaphragm integrally has a main portion and a single supporting portion supporting the main portion. The main portion is generally circular in plan view. The supporting portion is in the form of an arm extending sideward from the peripheral edge of the main portion, and the forward end portion thereof is fixed to the silicon substrate. Thus, the diaphragm is vibratile in a direction opposed to the surface of the silicon substrate in such a one-point support state that the main portion is supported by the single supporting portion. A back plate is arranged on a side of the diaphragm opposite to the substrate at a small interval from the diaphragm. The diaphragm and the back plate form a capacitor having the diaphragm and the back plate as counter electrodes.
When the diaphragm vibrates due to a sound pressure (sound wave) while a prescribed voltage is applied to the capacitor (between the diaphragm and the back plate), the capacitance of the capacitor changes, and voltage fluctuation between the diaphragm and the back plate resulting from the change of the capacitance is output as a sound signal.
The sensitivity of the silicon microphone is improved as the vibrational amplitude (displacement in a direction orthogonal to a sound pressure input surface) of the diaphragm with respect to the same sound pressure is increased. If the diaphragm remarkably vibrates and excessive stress is caused in the diaphragm, however, the diaphragm is broken due to the stress.
The vibrational amplitude (vibratility) of the diaphragm with respect to the same sound pressure can be reduced by increasing the number of supporting portions, for example. Depending on the arrangement of a plurality of supporting portions, however, the vibrational amplitude of the diaphragm with respect to the same sound pressure is extremely reduced to remarkably lower the sensitivity of the silicon microphone. When the diaphragm is supported by a plurality of supporting portions, therefore, the supporting portions must be arranged with due consideration.